I'm not sure what ATF stands for - American Tree Frog? He kinda looks like a Grey Tree Frog to me, and the stripes are a bit unusual but they look totally natural. Tree frogs do change color sometimes.
I do know that the your description of him "throwing up" sounds a lot like he's just shedding his skin - don't worry, every new frog owner freaks out when they see that for the first time. They'll writhe around and have a string of black goo stretching from their sides into their mouth (they eat their shed skin). If you ever see him doing that, don't bug him, I assure you he's fine.
This is what it looks like:
https://www.youtube.com/watch?v=Y8ghPWwvOxs